The purpose of the invention is more precisely to detect, at the neck ring of an object, any surface defects or flaws corresponding to material shortage on the surface called <<unfilled finish>>.
In the state of the art, a device is known to detect such defects comprising a light source providing an incident light beam illuminating the surface of the neck ring of a container. Said detection device also comprises a line scan camera positioned to receive the light beam reflected by the neck ring of the container. The presence of a defect disturbs light reflection which, depending upon the type of defect, causes light extinction or flare detectable by the line scan camera which is connected to an analysis and processing unit adapted for analysis the video signal delivered by the camera in order to determine the presence or absence of a surface defect and/or material shortage. With said device it is possible to detect unfilled finishes in particular which relate to material shortage on the surface. An unfilled finish corresponds to a hollow part in the surface of the neck ring which is normally planar or rounded. Said defects can be see in a dark or black image against a white background.
To ensure proper inspection of the neck ring surface of containers, control must be gained over the incident angle of the light flow with respect to the surface of the neck ring. For small-sized neck rings such as those of bottles, this incident angle can be controlled by changing the height of the light source as is proposed for example in patent U.S. Pat. No. 4,606,635 which describes a device for detecting defects on the neck ring of a container. Said device comprises an annular light source delimited by an inner cylinder and an outer cylinder defining between them a cylindrical outlet whose height can be adjusted through relative movement of the cylinders. Relative movement can be imparted to this light source with respect to the container to be inspected so as to adjust the angle of incidence of the diffuse light beam.
This device is not adapted for detecting defects on neck rings having large size surface areas, in particular on account of the angle of incidence which is too small and does not allow uniform lighting of the ring surface to be obtained. Also, for containers having neck rings whose surface is slightly inclined inwards or outwards, it proves to be insufficient to correct the angle of incidence solely by adjusting the height of the light source. Finally, it is to be noted that with said inspection device it is not possible to adapt to the different diameters of the neck rings found on containers to be inspected.
Also an apparatus is known through patent FR 2 596 523 for inspecting bottle caps, comprising a divergent annular light source positioned above the cap to be inspected. This apparatus comprises a first optical mask defining the radiation range of the light source and a second optical mask defining the field of vision of a photoelectric sensor.
With this apparatus it is possible to detect a defect on the lower part of a cap on a bottle neck. However, this apparatus is not adapted for detecting defects on the surface of the neck rings of containers which all have different slopes, widths and diameters. Also, with this apparatus it is not possible to achieve uniform illumination of containers having large surface areas.
Analysis of the state of the art leads to ascertaining that a technique is required with which it is possible to control the angle of incidence and/or the width of a uniform light flow with respect to the neck ring surface of the containers, in order to adapt to the different slopes, widths and diameters of container neck rings.